[3.13] bpo-44172: Keep reference to original window in curses subwindow objects (GH-26226) (GH-133370)

The X/Open curses specification[0] and ncurses documentation[1]
both state that subwindows must be deleted before the main window.

Deleting the windows in the wrong order causes a double-free with
NetBSD's curses implementation.

To fix this, keep track of the original window object in the subwindow
object, and keep a reference to the original for the lifetime of
the subwindow.

[0] https://pubs.opengroup.org/onlinepubs/7908799/xcurses/delwin.html
[1] https://invisible-island.net/ncurses/man/curs_window.3x.html
(cherry picked from commit 0af61fe2f41048d66b0a973bbff056690446d3df)

Co-authored-by: Michael Forney <mforney@mforney.org>